Field of the Invention
The present invention relates to a heat-screening glass which has a chemical- and wear-resistant protective film as the outermost layer on a transparent sheet glass.
Description of the Prior Art
It is a recent practice to use a heat-screening glass coated with a heat-screening film in order to reduce the influx of solar energy through building and automotive windows. A known example of such glass is the one which utilizes the property that heat rays are reflected by a film of metal (such as Cu, Al, and Ag) or a film of metal nitride (such as titanium nitride and zirconium nitride). The other known example is the one which has, for reflection of heat rays, alternately formed films of high-refracting and low-refracting materials. If they are to be used alone, they should have good mechanical, wear, and chemical resistance, among others, scratch resistance.
To meet this requirement, there was proposed a heat-screening glass which has a thick oxide film, for example, an SiO.sub.2 film thicker than 1 .mu.m, as the outermost layer, formed on the coating layer. (See Japanese Patent Laid-open No. 206333/1988.) There was also proposed a protective film of ZrB.sub.x O.sub.y, SnO.sub.2, or SiO.sub.2. (See Japanese Patent Laid-open No. 314163/1989.)
However, the protective film of SiO.sub.2 thicker than 1 .mu.m has a disadvantage of taking a long time for its coating, which leads to low productivity and high production cost. The protective film of SnO.sub.2 is poor in chemical resistance, and the protective film of ZrB.sub.x O.sub.y lacks reproducibility.